The present invention relates to a video game interface technique and, in particular, to a method and apparatus for determining an X-Y shot position with a light gun on various styles of Liquid Crystal Display (LCD) and Plasma Displays.
Recent advances in television and computer monitors that use LCD flat panel and plasma display systems have made current Cathode Ray Tube (CRT) display light guns obsolete. Past light guns and pen lights relied on the detection of a single horizontal and vertical retrace to detect a shoot position in X and Y coordinates. New display systems such as LCD and Plasma displays do not use a consistent horizontal and vertical retrace pulse as required by current light guns or light pens.
A CRT comprises a large vacuum glass tube in which a static charge is applied to the front of the display and electrons are released by an electron gun in the back of the tube. The electrons are attracted to the charge at the front of the tubes. When the attracted electrons strike the phosphorous coating on the front inside of the tube, the phosphorous glows which produces visual color. The electronic pulse is generated based on the modulated alternating current from the power supply. Typical North American power supply uses 60 hertz alternating electrical current. CRT displays use this 60 hertz alternating current to generate a saw tooth electronic pulse that in turn controls the timed release of electrons from the electron gun.
The electronic circuit in a CRT display system that generates the saw tooth pulse is called a fly-back transformer. The fly back transformer generates a saw tooth voltage increase that in turn increases or decreases the strength of an electro-magnet. The increasing strength of the electro-magnet pulls the electron beam across a horizontal scan line that in turn produces a visual line across the CRT display. A horizontal pulse, generated by the fly back transformer, causes the voltage to drop and in turn causes the electro-magnetic strength to decrease which in turn causes the horizontal scan to start at the beginning of the line again. Each time a line is drawn horizontally, a similar process pulls the electron beam down one line that causes repeated horizontal scan lines to travel across and down the front of the CRT display. A vertical retrace pulse at the bottom-end causes the scan to start at the top-left corner of the display for a next frame.
Video games are software programs that use a video game console system to translate the game data. A controller allows a game player to move within the rendered video game program. Many video games include the use of a light gun, or a controller with a shoot button, to simulate shooting with a gun or other weapon.
Conventional light gun technologies detect the start of the vertical retrace pulse via electronic connections and have a photo-detector on the light gun, that detects the horizontal retrace line as the brightest phosphorous point on the screen. A mathematical calculation is applied in the light gun electronic circuit to calculate an X-Y position of the point on the screen that the gun has pointed at.
Current Liquid Crystal and Plasma displays do not use such electron beams to draw a screen image and therefore current light gun technologies do not work with such display systems. A need exists for a light gun that is able to determine an X and Y shot position on a Liquid Crystal or Plasma screen.